Such tools are generally known. For example, German OS No. 23 06 780 (corresponding to GB No. 1 392 704), shows a toothed base member coated with diamond grains on its flanks. A coating with grains of a cubic boron nitride (CBN) is described in German OS No. 32 02 695 (corresponding to GB No. 2 113 584).
The coating of the tool tooth flanks is, however, very complicated and thus expensive in particular in the case of tools having a large tooth count. In particular, the grinding of diamond coatings requires an enormous amount of time. If tools are to be dressed, which are needed for the precision working of only a small production run of work gears, then the total costs are often too high because of the high costs for the dressing tool.
It is therefore also already known to leave out entire teeth in gearlike dressing tools provided with a coating of extremely hard abrasive grains like diamond or CBN (German OS No. 33 46 189, which corresponds to U.S. Pat No. 4,677,962), so that only a smaller number than the nominal tooth count needs to be coated and ground. A disadvantage of these tools is, however, that they must be guided in the correct position into meshing engagement with the precision-working tool which is to be dressed. This demands partly rather complicated auxiliary means, like position indexing, point disengagement, guide wheels, etc.
The basic purpose of the invention is to provide a dressing tool of the abovedescribed type, avoiding the abovementioned disadvantages, which dressing tool can be manufactured quickly and inexpensively.
To attain the purpose, a dressing tool is provided wherein the coated teeth are provided in only one sector of the entire gear, wherein the remaining teeth are not coated and wherein the thickness of the noncoated teeth is at least approximately equal to the thickness of the coated teeth including the coating. The sector having the coated teeth could thereby theoretically extend from one tooth to a maximum z-1, wherein z is the total tooth count of the dressing tool. However, the 90.degree. to 120.degree. range for coated teeth has proven to be advantageous. This means that approximately one fourth to one third of all teeth have the coating, and that the thickness of the noncoated teeth must be approximately equal to the thickness of the coated teeth including the coating, because the dressing tool is usually used in the rolling method and unevenly thick teeth would lead to incorrect mating relationships.
A development wherein a sector with the coated teeth is releasably secured to the remaining part of the dressing tool, makes the manufacture of the teeth, which are of different thickness prior to the coating, easier.
The important advantage of the inventive dressing tool is the quicker and thus less expensive manufacturing capability compared with the known tools and the flexible possibility of use resulting therefrom. The life of the new dressing tool is shorter than the life of dressing tools wherein all of the teeth are coated. However, since the frequency of use of the inventive dressing tool is at the same time also correspondingly less, this disadvantage balances out again.
The field of application of the inventive dressing tool is the dressing of gearlike tools on socalled hard shaving machines, in which the spindle receiving this tool and the spindle receiving the work gear to be worked by it are connected through guide gears (German OS No. 33 04 980, which corresponds to U.S. Pat. No. 4,689,918). Due to the kinematic relationships during the hard shaving, the noncoated teeth are not worked during the dressing operation by the teeth of the abrasive tool to be dressed, since the latter teeth are profiled by the equally thick coated teeth so that the distance between the teeth of the dressing tool and tool to be dressed is maintained.